In many industrial installations valves are used in circumstances where their incorrect operation could lead to accidents resulting in serious damage or injury. For example, many factories utilise pressure vessels which need to be entered by workers for maintenance and/or repair. It is essential that valves controlling supply of fluid under pressure to such vessels are locked in the shut or closed position when such maintenance or repair is taking place. In other situations it may be important for safety purposes that a valve is not closed. For example, dosing a valve may prevent adequate ventilation.
Typically butterfly valves, ball valves and plug valves are used under the circumstances referred to. Butterfly valves, ball valves and plug valves typically require only a quarter turn of an operating spindle between closed and open positions. However, some ball valves require rotation of an operating spindle through 180 degrees between closed and open positions. A valve actuator is typically used to rotate an operating spindle.
Past attempts to address the abovementioned safety issues have involved placing a hood over the valve actuator. However, the hoods are typically cumbersome to use and not always effective.
The inventor of the present invention developed the valve locking device which is described in South African Patent No. 97/10910 for the purpose of addressing the abovementioned safety issues. The valve locking device of South African Patent No. 97/10910 generally comprises a rigid metal u-shaped frame which has a cross plate that is welded to extend across the mouth of the u-shaped frame. The u-shaped frame is designed to slidably receive a spindle engaging plate that has a slot formed in one of its ends.
The u-shaped frame is designed to mount between a valve and its corresponding valve actuator in the process of assembling the valve and valve actuator. The slot of the spindle engaging plate is designed so that it receives a square sectioned spindle of the valve, which extends between the valve and valve actuator, when the spindle engaging plate is appropriately received in the u-shaped frame, Rotation of the spindle is prevented when the spindle is positioned within the slot of the spindle receiving plate. The cross plate and spindle engaging plate have corresponding holes to enable the spindle engaging plate to be fixed relative to the cross plates, ensuring that the spindle ngaging plate remains fixed relative to the u-shaped frame.
While the valve locking device of 97/10910 addresses the abovementioned safety issues, the inventor estimates that it may be prone to failure after 100 cycles at approximately 50% torque.
It is therefore desirable to provide an improved valve locking device.